Method for reducing coefficient of thermal expansion in chip attach packages

ABSTRACT

A simple, inexpensive, drillable, reduced CTE laminate and circuitized structures comprising the reduced CTE laminate, is provided. One embodiment of the reduced CTE laminate comprises: from about 40% to 75%, preferably from about 55% to 65%, by weight resin; from about 0.05% to 0.3%, preferably from about 0.08% to 0.10%, by weight curing agent; from about 25% to 60%, preferably from about 30% to 40%, by weight, woven cloth; from about 1% to 15%, preferably from about 5% to 10%, by volume, non-woven quartz mat. The method for making reduced CTE laminate and laminate structures comprises the following steps: providing non-woven quartz mat; providing a prepreg, preferably B-stage cured to not more than about 40%, preferably not more than 30% of full cure; sandwiching the non-woven quartz mat between two layers of prepreg, and reflowing the resin of the prepreg into the quartz mat.

RELATED APPLICATIONS

[0001] This application is a divisional of application Ser. No.09/265,210, filed on Mar. 10, 1999, which is a divisional application ofSer. No. 08/874,902, filed on Jun. 13, 1997, now U.S. Pat. No.6,136,733.

[0002] The presence of different materials within a chip attach package,leads to different coefficients of thermal expansion within the package.The differential expansion can cause warpage within these packages,including flip chip attach packages. This warpage can fatigue chipattach joints and also cause chip cracking.

[0003] Attempts have been made to reduce the warpage of the package;however they require additional, often expensive process steps. Materialshaving a low coefficient of thermal expansion, like molybdenum,combinations of metals like copper-invar-copper, or other exotic organicreinforcements such as Kevlar, have been employed in packages to reducethe coefficient of thermal expansion. Kevlar, however, absorbs moisture.Copper-invar-copper is expensive and difficult to drill. Molybdenum isexpensive, tough to drill, and hard to etch with conventional etchants.

[0004] Attachments such as stiffeners or encapsulants on top of the chipare often employed to counteract warpage. However, encapsulants and topstiffeners add extra processing steps, cost, complexity and they occupyadditional space.

[0005] Instead of glass cloth in the dielectric layers of a package,woven quartz cloth has been used in an attempt to lower the coefficientof thermal expansion. However, dielectric which employs woven quartzcloth is thick and heavy which limits the usefulness of the prepreg.Furthermore, laminates made with such quartz prepreg are difficult todrill due to the hardness of the quartz and the thickness of the quartzyarn bundles.

[0006] While the coefficient of thermal expansion of dielectric layershaving resin as a base can be reduced by reducing the resin content,substantial reductions in resin content effect the designed dielectricperformance by increasing the dielectric constant of the material, whichoften necessitates a compensating design change in the package or thedielectric itself.

[0007] It would be desirable to be able to reduce the warpage of chipattach packages by a method which does not employ expensive, difficultto drill materials.

SUMMARY OF THE INVENTION

[0008] The present invention provides a simple, inexpensive, drillable,reduced CTE laminate and circuitized structures comprising the reducedCTE laminate. The reduced CTE laminate comprises: from about 40% to 75%,preferably from about 55% to 65%, by weight resin; from about 0.05% to0.3%, preferably from about 0.08% to 0.10%, by weight curing agent; fromabout 25% to 60%, preferably from about 30% to 40%, by weight, wovencloth; from about 1% to 15%, preferably from about 5% to 10%, by volume,non-woven quartz or non-woven glass mat.

[0009] The present invention also generally relates to a method forreducing the CTE of circuitized structures, and to methods for makingreduced CTE laminate and circuitized structures comprising reduced CTElaminate.

[0010] The method for making reduced CTE laminate comprises thefollowing steps: providing non-woven quartz or non-woven glass mat;providing a prepreg, preferably B-stage cured to not more than about40%, more preferably not more than 30%, most preferably not more than20% of full cure; sandwiching the non-woven mat between two layers ofprepreg, and reflowing the resin of the prepreg into the non-woven mat.Optionally, the reduced CTE laminate is sandwiched between two layers ofmetal, preferably copper.

BRIEF DESCRIPTION OF THE FIGURES

[0011]FIG. 1 is a cross sectional drawing of the reduced CTE laminate;and

[0012]FIG. 2 is a cross sectional drawing of a circuitized structurecontaining the reduced CTE laminate structure.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention provides a simple, inexpensive, drillable,reduced CTE laminate and circuitized structures comprising the reducedCTE laminate. The reduced CTE laminate comprises: from about 40% to 75%,preferably from about 55% to 65%, by weight resin; from about 0.05% to0.3%, preferably from about 0.08% to 0.10%, by weight curing agent; fromabout 25% to 60%, preferably from about 30% to 40%, by weight, wovencloth; from about 1% to 15%, preferably from about 5% to 10%, by volume,non-woven quartz fiber mat.

[0014] The present invention also generally relates to a method forreducing the CTE of circuitized structures, and to methods for makingreduced CTE laminate and circuitized structures comprising reduced CTElaminate.

[0015] The method for making reduced CTE laminate comprises thefollowing steps: providing non-woven quartz fiber mat; providing aprepreg, preferably B-stage cured to not more than about 40%, morepreferably not more than 30%, most preferably not more than 30% and notless than 5%, preferably not less than 10%, of full cure; sandwichingthe non-woven mat between two layers of prepreg, and reflowing the resinof the prepreg into the nonwoven mat.

[0016] A particular advantage of the present invention is that thenon-woven mat can be incorporated during the assembly of an otherwiseconventional laminate, to lower the CTE of the laminate. Thus,conventional laminates which have already been designed for use in aparticular circuitized structure or use in a particular manufacturingline, do not have to be redesigned, or reengineered in order to lowerthe CTE, as would be necessitated with other methods of lowering the CTEin the laminate.

[0017] A further advantage of the present reduced CTE laminate is thatadditional resin need not be employed beyond the amount used inconventional laminates. In addition, the overall thickness of thereduced CTE laminate is not increased significantly, and thus thethickness of packages which comprise the reduced CTE laminate are notincreased significantly.

[0018] The CTE of the reduced CTE laminate is adjusted as desired,preferably by varying the weight, density, or the number of plies of thenon-woven mat employed. To lower the CTE of a laminate, the “amount” ofthe non-woven mat is determined based on the amount of glass cloth andthe amount of resin to be present in the laminate.

[0019] In one embodiment of the invention, the CTE of the reduced CTElaminate is determined according to the following formula, designated“formula A”, a weighted average for determining VOL and/or CTE:$\underset{\quad {CORE}}{{CTE}_{{comp}/}} = \frac{\begin{matrix}{{\left( {CTE}_{R} \right)\left( {MOD}_{R} \right)\left( {VOL}_{R} \right)} + {\left( {CTE}_{G} \right)\left( {MOD}_{G} \right)\left( {VOL}_{G} \right)} +} \\{{\left( {CTE}_{C} \right)\left( {MOD}_{C} \right)\left( {VOL}_{C} \right)} + {\left( {CTE}_{Q} \right)\left( {MOD}_{Q} \right)\left( {VOL}_{Q} \right)}}\end{matrix}}{\begin{matrix}{{\left( {MOD}_{R} \right)\left( {VOL}_{R} \right)} + {\left( {MOD}_{G} \right)\left( {VOL}_{G} \right)} +} \\{{\left( {MOD}_{C} \right)\left( {VOL}_{C} \right)} + {\left( {MOD}_{Q} \right)\left( {VOL}_{Q} \right)}}\end{matrix}}$

[0020] where:

[0021] CTE_(R)=CTE of the resin,

[0022] MOD_(R)=modulus of resin,

[0023] VOL_(R)=Volume fraction of resin,

[0024] CTE_(G)=CTE of woven glass cloth,

[0025] MOD_(G)=Modulus of woven glass cloth,

[0026] VOL_(G)=Volume fraction of glass cloth,

[0027] CTE_(C)=CTE of copper,

[0028] MOD_(C)=Modulus of copper,

[0029] VOL_(C)=Volume of fraction of copper,

[0030] CTE_(Q)=CTE of mat fiber, quartz,

[0031] MOD_(Q)=Modulus of mat fiber, quartz,

[0032] VOL_(Q)=Volume fraction of fiber mat.

[0033] The Modulus values are intrinsic to their respective materials,as is well known in the art. The volume fractions are determined bymeasuring the volume of each component and calculating the volumefraction.

[0034] The above formula expressed as formula B, can also be employed tocalculate the amount of non-woven quartz mat needed to be added to alaminate and/or laminate structure to arrive at a desired CTE for thepackage. Thus, if a package CTE of X is desired, the VOL_(Q) is obtainedby the following formula B: ${VOL}_{Q} = \frac{\begin{matrix}\begin{matrix}{{\left( {CTE}_{R} \right)\left( {MOD}_{R} \right)\left( {VOL}_{R} \right)} + {\left( {CTE}_{G} \right)\left( {MOD}_{G} \right)\left( {VOL}_{G} \right)} +} \\{{\left( {CTE}_{C} \right)\left( {MOD}_{C} \right)\left( {VOL}_{C} \right)} - {\left( {CTE}_{COMP} \right)\left( {MOD}_{R} \right)\left( {VOL}_{R} \right)} -}\end{matrix} \\{{\left( {CTE}_{COMP} \right)\left( {MOD}_{G} \right)\left( {VOL}_{G} \right)} - {\left( {CTE}_{COMP} \right)\left( {MOD}_{C} \right)\left( {VOL}_{C} \right)}}\end{matrix}}{{\left( {CTE}_{COMP} \right)\left( {MOD}_{Q} \right)} - {\left( {CTE}_{Q} \right)\left( {MOD}_{Q} \right)}}$

[0035] Typical values of the factors of one embodiment of the inventionare:

[0036] CTE_(R)=CTE of the resin, is 69 ppm°/C.

[0037] MOD_(R)=modulus of resin, is 6.5 GPA

[0038] VOL_(R)=Volume fraction of resin is 51.3%

[0039] CTE_(G)=CTE of E-glass woven glass is 5.5 ppm°/C.

[0040] MOD_(C)=modulus of E-glass woven cloth is 70 GPA

[0041] VOL_(E)=Volume fraction of glass cloth is 31.9%

[0042] CTE_(C)=CTE of copper is 17 ppm°/C.

[0043] MOD_(C)=modulus of copper is 117 GPA

[0044] VOL_(C)=Volume of fraction of copper is 10.21%

[0045] CTE_(Q)=CTE of non woven mat fiber, quartz, is 0.54 ppm°/C.

[0046] MOD_(Q)=Modulus of mat fiber, quartz is 70 GPA

[0047] VOL_(Q)=Volume fraction of fiber mat is 6.6%

[0048] The CTE reduction is achieved by adding single or multiplenon-woven quartz mats during the fabrication of the reduced CTE laminateor reduced CTE laminate structure.

[0049] The Non-Woven Mat

[0050] The non-woven mat is non-woven quartz mat or non-woven glass mat.The non-woven mat has randomly oriented fibers held together by binder,preferably from about 5 to 15% binder by weight of the mat. Preferablythe binder is for example epoxy resin or polyvinyl alcohol. Preferablythe fibers have an average length of about 0.25 inch up to 3 inches,more preferably about 0.5 inches, and preferably have an averagediameter of from about 5 to 12, more preferably from about 6 to 10, mostpreferably about 9 microns. The non-woven mats preferably have a weightper unit area of from about 10 g/m² to 80 g/m², more preferably about 17g/m² to 34 g/m². The non-woven mats prior to being impregnated withresin, have preferably at least about 50%, more preferably at leastabout 75%, void space. Preferably, the non-woven mats have no more thanabout 95% void space prior to being impregnated with resin.

[0051] After the non-woven mats are impregnated with resin, the voidspaces are substantially filled with resin to form a resin filled matrixwhich surrounds the mat fibers. However, when insufficient amount ofprepreg is used in relation to the non-woven mat fiber or conversely anexcess of non-woven mat fiber is used in relation to the resin,insufficient resin from the prepreg is available to fill the void spaceswhich are initially present in the non-woven mat. As a result some voidspaces remain in the resin impregnated mat; such void spaces in theresin impregnated mat are referred to herein as “voids”. Voids presentin the circuitized structure detract from the electrical insulationresistance reliability of such structure. Preferably, the reduced CTElaminate and thus the circuitized structure into which the reduced CTElaminate is incorporated, has from 0-5%, more preferably from about 0 to2% by volume, voids, from about 70 to 90% by volume matrix, and fromabout 5 to 30% by volume quartz fiber.

[0052] The Prepreg

[0053] The prepreg formulation is conventional; the prepreg has a resincontent of from about 40% to about 75%, preferably from about 55% to 65%by weight, and a woven cloth content of from about 25 to 65%, preferablyfrom about 20% to 30% by weight. Optionally a cure accelerator is used.The resins are conventional thermoset resins employed in prepregincluding for example, epoxy resin, polyimide resins, triazine resins,bis-maleimide-triazine resins, and cyanate ester resins. Suitable epoxyresin is available under the designation “LZ8213” from Ciba GeigyCompany. The woven cloth serves as a reinforcement and as a resincarrier. The woven cloth is conventional, and includes for example,cloth composed of non-conductive organic fibers, inorganic fiber such asglass, alumina fiber, S, D, K and E Glass. E Glass is particularlysuitable; it is composed of from about 52 to 56% by weight silicondioxide, from about 16 to 25% by weight calcium oxide, from about 12 to16% by weight aluminum oxide, from about 8 to 13% by weight boron oxide,from about 0 to 1% by weight sodium oxide and potassium oxide, and fromabout 0 to 6% by weight magnesium oxide. Woven cloth is preferredbecause it absorbs less resin, and because it provides betterdimensional stability than a non-woven material. Suitable “E glass” isthe 1080 style, which is commercially available. Suitable curingaccelerators are conventional such as, for example, 2-methylimidazole,BMDA, TMBDA, 2-ethyl-4-methylimidazole, 2-phenylimidazole.

[0054] Method of Forming Prepreg

[0055] The prepreg is made according to conventional techniques. Theglass cloth is coated, or impregnated, with the resin by dipping orotherwise passing the glass cloth through a solution containing theresin, solvent, and a curing agent. The resin impregnated glass cloth isthen run through metering rolls to remove excess resin. The resinimpregnated glass cloth is then dried in an oven at from about 120-170°C., to remove the solvent and at the same time to effect a B-stage cure.B-stage cure is a partial cure of the resin. Conventionally, the prepregis b-stage cured to about 30 to 40%; however to make the laminates ofthe present invention, it is preferred that the prepreg is only about 20to 30% cured.

[0056] Method of Forming Reduced CTE Laminate

[0057] Preferably the non-woven mat is sandwiched, preferably bylamination, more preferably by vacuum lamination, between two layers ofprepreg and the prepreg is heated for sufficient time and temperature sothat the resin in the prepreg reflows and flows into the mat, wettingthe mat. Methods which involve immersing the non-woven mat in a solutionof resin are less preferred since the non-woven mat absorbs excessiveresin.

[0058] Preferably the non-woven mat is applied to the prepreg bylamination, more preferably vacuum lamination. The initial vacuum of thelamination cycle removes the air trapped in the void spaces of thenon-woven mat. The open, low density nature of the non-woven mat allowsthe resin to flow in and surround the fibers of the non-woven mat. Sincethe non-woven mat is sparsely populated with fibers it wets well; this“dry impregnation” is not possible with ordinary woven fabrics whichhave yams composed of hundreds of parallel fibers. Preferably thelamination is at about 180 to 300° C. and pressures of about 500 to 1000psi. Good results have been obtained by vacuum lamination at 185° C.,and 750 psi. The resulting reduced CTE laminate is shown in FIG. 1.

[0059] As shown in FIG. 1, reduced CTE laminate 10 is comprised ofprepreg layers 12 and 14, and non-woven mat 16 disposed between prepreglayers 12 and 14. Prepreg layers 12 and 14 contain glass layers 18 and20.

[0060] Reduced CTE laminate is typically further laminated to additionallayers of prepreg, copper foil and optionally additional layers ofnon-woven mat, to form laminate structures such as, for example, coresor composites. The reduced CTE laminate and/or the laminate structuresare then used to fabricate circuitized structures such as, for example,printed circuit boards, cards, chip carriers, organic single chipmodules, organic multi-chip modules, and interposer cards by employingconventional techniques. For example, as shown in FIG. 2, a circuitizedstructure 100 is comprised of laminate structure 112, which is comprisedof a signal layer 114 and power or ground plane layer 116; dielectriclayer 118, which is disposed between signal layer 114 and power orground plane layer 116, is comprised of prepreg layers 120 and 122.Preferably non-woven mat 124 is disposed between prepreg layers 120 and122. Adjacent to the circuitry layer 116 is the core 126 which iscomprised of prepreg layers 128, 130, 132 and 134. Preferably non-wovenmats 136, 138 and 140 are interspersed between the glass layers 128 130,132 and 134 of the core 126. Power or ground plane layer 142 is disposedadjacent to prepreg layer 134. Dielectric layer 144 is disposed betweentower or ground plane layer 142 and signal layer 146. Dielectric layer144 is comprised of glass layers 148 and 150, preferably non-woven mat152 is interspersed between prepreg layers 148 and 150. Signal layer 114and power or ground plane layers 116 and 142 are interconnected byconventional structures such. as conductive through holes and vias, notshown. Chip (not shown) is disposed atop layer 114.

[0061] The following examples are illustrative and not intended to limitthe scope of the invention.

EXAMPLE 1

[0062] Prepreg was fabricated to provide a prepreg having about 60% byweight epoxy resin, 0.1% by weight curing accelerator 2-methyl imidizoleand 40% by weight E-glass 1080, and b-stage cured to about 20 to 30%.Next, a multilayered structure was assembled which comprised a layer ofcopper sheet, a first layer of prepreg atop the copper, a second layerof prepreg atop the first layer of prepreg, a layer of non-woven quartzmat, a third and fourth layer of prepreg and finally a second layer ofcopper sheet. The non-woven quartz mat was about 0.004 inches thickbefore lamination, had a weight per unit area of about 17 g/m² and wasobtained from Technical Fiber Products Company. The multilayeredstructure was then vacuum laminated in a Wabash lamination press, at185° C. for about 120 minutes at around 750 psi, to provide a reducedCTE laminate, in this case a laminate core. The copper layers on theoutside of the core were then etched to form the circuit features usingconventional techniques.

[0063] Then a laminate structure comprising the circuitized laminatedcore was fabricated which comprised an outside, third layer of copper, afifth and sixth layer of prepreg, having about 67% resin, adjacent tothe third layer of copper, and the circuitized laminate core positionedadjacent to the sixth layer of prepreg. Atop the circuitized core were aseventh and eighth layer of prepreg and fourth layer of copper sheetadjacent to the seventh and eight layer of prepreg. The multi-layeredstructure was then placed in the vacuum lamination press for about 120minutes, at 185° C. and 750 psi to provide a laminate structure.

[0064] The CTE of the resulting laminate structure was measured andfound to be 18.52 ppm/° C. in the x-y direction and 60 ppm/° C. in the zdirection. The resulting laminate structure had a total thickness ofabout 25.9 mils.

EXAMPLE 2

[0065] A reduced CTE laminate structure was made as in example 1, exceptthat the core lacked a non-woven mat. Instead a non-woven quartz mat wasemployed between the fifth and sixth prepreg layers, and between theseventh and eight prepreg layers, so that 2.3% rather than 1.2% of thelaminate structure was quartz non-woven mat. The resulting compositestructure had a total thickness of about 26.2 mils.

EXAMPLE 3

[0066] A reduced CTE laminate structure was made as in example 1, exceptthat a non-woven quartz mat was also employed between the fifth andsixth prepreg layers, and between the seventh and eight prepreg layers,so 3.4% rather than 1.2% of the laminate was quartz non-woven mat. Theresulting laminate structure had a total thickness of about 26.5 mils.

EXAMPLE 4

[0067] A reduced CTE laminate was made as in example 2, except that anon-woven quartz mat was employed between the first and second prepreglayers, and between the third and fourth prepreg layers, so 4.5% ratherthan 1.2% of the laminate was quartz non-woven mat. The resultinglaminate had a total thickness of about 26.8 mils.

EXAMPLE 5

[0068] A reduced CTE laminate was made as in example 3, except that anon-woven quartz mat was employed between the first and second prepreglayers, and between the third and fourth prepreg layers, so 5.6% ratherthan 1.2% of the laminate was non-woven quartz mat. The resultinglaminate had a total thickness of about 27.1 mils.

EXAMPLE 6

[0069] A reduced CTE laminate structure was made as in example 1 exceptthat a thicker non-woven quartz mat was employed. The weight per unitarea of the mat was 34 g/m² rather than 17 g/m². Thus, 2.3% rather than1.2% of the laminate structure was quartz non-woven mat. The resultinglaminate structure had a total thickness of about 26.2 mils.

EXAMPLE 7

[0070] A reduced CTE laminate structure composite was made as in example2 except that a thicker non-woven quartz mat was employed. The weightper unit area of the mat was 34 g/m² rather than 17 g/m². Thus, 4.5%rather than 2.3% of the laminate structure was quartz non-woven mat. Theresulting structure laminate structure had a total thickness of about26.8 mils.

EXAMPLE 8

[0071] A reduced CTE laminate was made as in example 3 except that athicker non-woven quartz mat was employed. The weight per unit area ofthe mat was 34 g/m² rather than 17 g/m². Thus, 6.6% rather than 3.4% ofthe composite laminate was quartz non-woven mat. The resulting laminatestructure had a total thickness of about 27.4 mils.

EXAMPLE 9

[0072] A reduced CTE laminate was made as in example 4 except that athicker non-woven quartz mat was employed. The weight per unit area ofthe mat was 34 g /m² rather than 17 g/m². Thus, 8.6% rather than 4.5% ofthe laminate structure was quartz non-woven mat. The resulting laminatestructure had a total thickness of about 28.0 mils.

EXAMPLE 10

[0073] A reduced CTE laminate was made as in example 5 except that athicker non-woven quartz mat was employed. The weight per unit area ofthe mat was 34 g/m² rather than 17 g/m². Thus, 10.6% rather than 5.6% ofthe laminate structure was quartz non-woven mat. The resulting laminatestructure had a total thickness of about 28.6 mils.

COMPARATIVE EXAMPLE A

[0074] A conventional prepreg was made as in example 1 except the resinwas cured to 30-40%. The laminate structure was made as in example 1except without non-woven quartz mat. The CTE of this conventionallaminate composite was 19.01 ppm/° C. in the x-y direction and 65 ppm/°C. in the x-y direction and 65 ppm/° C. in the z direction. Thethickness was 25.6 mils. TABLE I EFFECT OF NON-WOVEN MAT ON CTE % QuartzMat CTE Example (volume) (ppm/° C.) CTE Delta control/comp A 0 19.01 11.2 18.52 −0.49 2 2.3 18.06 −0.95 3 3.4 17.61 −1.4 4 4.5 17.20 −1.81 55.6 16.79 −2.22 6 2.3 18.06 −0.95 7 4.5 17.20 −1.81 8 6.6 16.41 −2.60 98.6 15.70 −3.31 10  10.6 15.04 −3.97

[0075] As can be seen from Table 1, the non-woven quartz mat reduced theCTE of each of the laminate composites or each of the examples. As shownin example 10, by incorporating the non-woven mat at several places inthe laminate structure, a reduction of about 4 ppm is achieved. Even areduction of 1 or 2 ppm in the coefficient of thermal expansion of thecomposite laminate can significantly reduce the amount of warpage in thechip carrier package.

[0076] Thus, by incorporating a non-woven quartz mat into the laminateand or laminate structure, the coefficient of thermal expansion in thelaminate and/or laminate structure is reduced thereby improving thefunction of the overall package.

What is claimed is:
 7. A method for fabricating circuitized structures,comprising the following steps: a. providing a prepreg comprised ofwoven cloth impregnated with a resin and B-stage cured to not greaterthan about 20%; b. providing a non-woven quartz or non-woven glass mathaving void space content greater than about 50%; and c. laminating thenon-woven mat between two layers of the prepreg to reflow the resin soas to impregnate the non-woven mat with resin.
 8. The method of claim 7,wherein the lamination is vacuum lamination.
 9. The method of claim 7,wherein the mat void space content is greater than about 75%.
 10. Themethod of claim 7, wherein the mat void space content is greater thanabout 95%.
 19. The method of claim 7, wherein the non-woven mat is anon-woven quartz mat.
 20. The method of claim 7, wherein the non-wovenmat is a non-woven glass mat.
 27. The method of claim 7, wherein the twolayers of prepreg are B-stage cured to not more than about 30%.
 28. Themethod of claim 7, wherein the two layers of prepreg are B-stage curedto not more than about 40%.
 29. The method of claim 7, wherein thenon-woven mat has a weight and comprises randomly oriented fibers heldtogether by a binder, said binder comprising from about 5 to 15% of thenon-woven mat weight.
 30. The method of claim 29, wherein the fibershave an average length of from about 0.25 to about 3.0 inches.
 31. Themethod of claim 7, wherein the fibers have an average diameter of fromabout 5 to 12 microns.
 32. The method of claim 7 wherein the step ofproviding a non-woven mat comprises providing a single mat.
 33. Themethod of claim 7 wherein the step of providing a non-woven matcomprises providing a plurality of mats.
 34. The method of claim 7wherein the resin is an epoxy resin.
 35. The method of claim 7 whereinthe woven cloth is E-glass.
 36. The method of claim 7 wherein thenon-woven mat has a percent void space of from about 50 to 95% byvolume.